A large capacity (1 - 2 MkVA) driving system for variable-speed-driving an AC motor by a power converter (inverter, converter) (100, 200) in which GTO (gate turn-off) thyristors (111, 121, 211, 221) are used as switching devices. In this system, high frequency GTO thyristors are connected in series, power converters are multiplexed, the AC motor is used in its plural phases, instantaneous spatial vector PWM (pulse width modulation) control (310, 320) is performed, vector control (330) for the motor is performed, and a circuit (4) for recovering snubber energy for GTO thyristors and a power factor adjusting circuit (340) are provided. Thus, this driving system provides a torque ripple of 1% or less, speed response of 60 rad/sec or more, efficiency of 95% or more and power factor of 98% or more.
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